CSE373 Optional Section Java Collections 11/12/2013 Luyi Lu

Today’s Topic Java Collection Interface Generics Collections Usage Wrapper Class CSE 142/143 Collections Review List & Set Stack & Queue Map

Java Collection Interface Interface is just a type Learn how to look up Java Documentation of the standard library What are the basic operations? llection.html llection.html Iterable and Comparable To use for loop and define the rule how object stored is compared Not used in HW5, but good to know

Collections Declaration with Generic Types How? List v = new ArrayList (); List e = new ArrayList (); Can we construct List ArrayList ? NO! In Java, anything that is used as generics has to be convertible to Object Solution: Use Wrapper Class for primitive types. E.g. ArrayList Every primitive type has a corresponding wrapper class: Integer for int, Double for double, Character for char, Boolean for boolean, And so on BTW.. String is not a primitive type and String objects are immutable (Continue on next slide)

Collections Declaration with Generic Types Autoboxing and Unboxing Java will automatically "box" the ints for us (i.e., wrap them up in Integer objects) Java automatically "unboxes" the values for you, unwrapping the Integer objects and giving you the ints that are contained inside. List numbers1 = new ArrayList (); numbers.add(18); numbers.add(34); int product = numbers.get(0) * numbers.get(1);

Lists & Sets Difference? Sets don’t allow duplicates Client can control order over lists, no index (How to remove?) HashSet doesn’t keep order TreeSet keeps things in sorted order APIs List: Set: Different Types and their Tradeoffs List ArrayList LinkedList Set HashSet(fast) TreeSet Declaration: LinkedList l = LinkedList (); is not good style should be List l = LinkedList (); You can find all of them in JAVA API!

Stack & Queue Discussed in CSE373 APIs Stack Class: Stack s = new Stack (); Queue Interface: Queue q = new LinkedList ();

Map Dictionary that stores key/value pairs One to one relation Map can have two types.You can have V as Lists or other data structures E.g. Map > API: TreeMap and HashMap

Useful Info ArrayList vs. Linked List linkedlist-over-arraylist HashSet vs. TreeSet treeset Some material of this slide is credited to Stuart Reges’ CSE143 Notes